Capacitance Detection Circuit for Touch Devices
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Solution Overview
Problem
Existing self-capacitance detection architectures are inadequate for detecting large capacitance values, as they become saturated and fail to accurately detect capacitance changes in capacitive sensors with self-capacitance exceeding 200 pF, particularly those with self-capacitance up to 500 pF, due to the small change signals generated when touched.
Innovation Solution
A capacitance detection circuit that includes a charging circuit to set a voltage difference on a detection capacitor, a discharging circuit to release a controlled quantity of charges, and a signal detection circuit to determine capacitance changes by comparing the post-discharge voltage with a preset value, preventing saturation and enhancing detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the self-capacitance of capacitive sensors is increased to improve sensor performance and stability, then the sensor stability is improved, but the capacitance change signal when touched becomes extremely small and cannot be detected by existing detection circuits
Solution Approach 1:
The patent applies preliminary action by performing base capacitance cancellation before the actual touch detection. The cancellation circuit actively compensates for the large self-capacitance (500 pF) of the sensor, reducing it to a manageable level so that subsequent capacitance changes from touch can be detected with sufficient precision. This preliminary cancellation enables the system to maintain both sensor stability and detection precision.
Solution Approach 2:
The patent introduces a cancellation circuit as an intermediary component between the capacitive sensor and the detection circuit. This intermediary actively manages the large self-capacitance by providing a cancellation path that reduces the base capacitance to a level suitable for accurate touch detection. The cancellation circuit serves as a mediator that enables both high sensor stability and precise capacitance change detection.
2Device complexity
If existing self-capacitance detection architecture is used, then the device complexity is low, but the measurement precision fails when self-capacitance exceeds 200 pF
Solution Approach 1:
The patent segments the detection system into distinct functional modules: a cancellation circuit for base capacitance compensation, a detection circuit for capacitance change measurement, and a processing circuit for signal analysis. This segmentation allows each module to be optimized independently - the cancellation circuit handles the complex base capacitance reduction while the detection circuit maintains simplicity for measuring small changes, thus achieving high precision without excessive overall complexity.
Solution Approach 2:
The patent changes the operating parameters of the detection system by dynamically adjusting the cancellation circuit to compensate for variations in self-capacitance. The system adapts to different sensor capacitance values (from 50 pF to 500 pF) by modifying the cancellation mechanism, enabling high measurement precision across a wide range of capacitance values while maintaining reasonable device complexity.
3Reliability
If the capacitance of capacitive sensors is increased to 500 pF, then the sensor performance is improved, but the capacitance change signal when touched becomes extremely small (0.2 pF) and cannot be detected
Solution Approach 1:
The patent performs preliminary base capacitance cancellation to reduce the 500 pF self-capacitance to a manageable level before touch detection. This preliminary action ensures that the subsequent capacitance change signal (even as small as 0.2 pF) can be detected with sufficient precision, as the cancellation circuit has already prepared the sensor by reducing the baseline capacitance burden.
Solution Approach 2:
The cancellation circuit acts as an intermediary that bridges the gap between high sensor performance (500 pF self-capacitance) and detectable capacitance changes. It mediates the interaction by actively compensating for the large self-capacitance, thereby enabling the detection of extremely small touch-induced capacitance changes while maintaining the reliability benefits of high self-capacitance sensors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables the detection of capacitance changes in capacitive sensors with self-capacitance up to 500 pF, improving detection accuracy and supporting larger capacitance values while reducing signal saturation, thereby effectively addressing the limitations of existing architectures.
Implementation Method 1
a charging circuit, configured to charge a detection capacitor, so that a voltage difference value between two polar plates of the detection capacitor is a first preset voltage value
Implementation Method 2
a discharging circuit, configured to cause the charged detection capacitor to release a first quantity of charges, where the first charge quantity is smaller than a charge quantity corresponding to the first preset voltage value
Implementation Method 3
a signal detection circuit, configured to detect a voltage difference value between a voltage value on the detection capacitor after being discharged by the discharging circuit and a second preset voltage value to determine a capacitance change of the detection capacitor based on the voltage difference value
Data Source
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Figure 3
Figure 4~5
AI summary
A capacitance detection circuit, a touch apparatus, and a terminal device are provided. The capacitance detection circuit includes: a charging circuit, configured to charge a detection capacitor, so that a voltage difference value between two polar plates of the detection capacitor is a first preset voltage value; a discharging circuit, configured to cause the charged detection capacitor to release a first quantity of charges where the first charge quantity is smaller than a charge quantity corresponding to the first preset voltage value; and a signal detection circuit, configured to detect a voltage difference value between a voltage value on the detection capacitor after being discharged by the discharging circuit and a second preset voltage value to determine a capacitance change of the detection capacitor based on the voltage difference value. The capacitance detection circuit is capable of performing capacitance detection when the self-capacitance is large.